1. Field of the Invention
This invention pertains to valve assemblies, and more particularly to sanitary valves having field replaceable gaskets that are cleanable in place.
2. Description of the Prior Art
It has long been known to equip linearly actuated valves with relatively soft gaskets for contacting a valve seat to provide a tight seal. For Example, U.S. Pat. No. 107,841 discloses a facing of rubber or other elastic substance placed around an oblique or curved portion of the valve stem. U.S. Pat. No. 1,538,126 teaches the use of a copper cup-shaped bearing in conjunction with the beveled surface of a valve stem. The copper, being relatively soft, is able to closely conform to the contour of the valve seat. U.S. Pat. Nos. 3,326,520; 3,445,089; and 3,531,086 illustrate carburetor needle valves with tips of rubber or similar material for contacting and sealing the valve seat of a carburetor float chamber.
A common feature of prior art valve gaskets is the difficulty of replacing the gaskets in the field. Installing a new rubber or other elastic tip or facing requires stretching and drawing over relatively large projections on the valve stem. In addition, as exemplified by U.S. Pat. No. 3,531,086, a portion of the valve stem may be crimped to hold the rubber tip more or less permanently in place. In some other prior art designs, it is necessary to heat the gasket in order to work it onto the valve stem.
With a construction such as is illustrated in U.S. Pat. No. 1,538,126, it is necessary to mechanically disassemble the valve elements, such as cotter pins, nuts, and screws, in order to remove the gasket. The reverse operation must be performed to install the new gasket. These disassembly and reassembly operations are time consuming and inefficient.
As a result of the gasket replacement difficulties with prior art devices, it is common practice to replace both the valve stem and gasket as a unit. This is wasteful because usually only the gasket requires replacement.
A further problem with the aforementioned prior art valve stems and gaskets is that they are not suitable for food handling applications. Sanitary installations require the use of non-corrosive materials, such as stainless steel and certain synthetic plastics. Further, the equipment should be easily cleanable, because cleaning is non-productive. Ease of cleaning requires the use of components having a minimum number of crevices for food particles to lodge in during operation. In addition, built-up particles must be easily flushable during cleaning. Ideally, machinery, including valve elements, for handling consumable products should be cleanable without the necessity of any disassembly and reassembly, i.e., the machinery should be cleanable with all the components in place. The prior art valve elements contain crevices that can trap food particles, and the crevices cannot be cleaned without laborious disassembly and reassembly.
Thus, a need exists for a sanitary valve assembly that incorporates a field replaceable gasket for sealing against the valve seat and that is quickly and efficiently cleanable in place.